The present invention relates to a waste plastic dechlorination system for removing toxic chlorine from vinyl chlorides in order to form solid fuels from waste plastics containing vinyl chlorides.
In order to form solid fuels from waste plastics containing vinyl chlorides, it is necessary to carry out a pretreatment to remove hydro-chloride gas normally produced at thermal decomposition of vinyl chlorides. When the formed solid fuel is burned, not only hydrogen chloride, but highly poisonous substances, such as dioxin, are also formed, unless the dechlorination treatment of waste plastics is carried out. As described in Japanese Patent Laid-Open No. 5-245463, the dechlorination treatment of waste plastics is carried out by utilizing the property that vinyl chlorides are thermally decomposed at about 300xc2x0 C. to liberate hydrogen chloride. However, the system disclosed in Japanese Patent Laid-Open No. 5-245463 can treat only vinyl chlorides having specific compositions.
Practical waste vinyl chlorides contain a substance causing the production of phthalic anhydride, i.e., a plasticizer. When a vinyl chloride contains such a plasticizer, the dechlorination rate is reduced to about 96%.
If the dechlorination rate remains low, the formed solid fuel cannot be used as a fuel since hydrochloric acid and dioxin are produced when the fuel is burned. Moreover, since phthalic anhydride is crystallized at a low temperature, there is also a problem in that pipes will be plugged clogged with the phthalic anhydride.
In addition, some vinyl chlorides are contained in waste plastics that have unusual shapes which are difficult to treat, such as bottle shapes or block shapes. In practice, these waste plastics are broken up to carry out the dechlorination process. In a conventional system, it is not possible to input waste plastics to the system unless the waste plastics are broken up into very fine particles. An economical particle size is a few centimeters. In order to break up the waste plastics to an even finer size, a separate shredder would be required. The shredded plastics are bulky since the plastics contain a large quantity of air, and the heat transfer rate is bad. Therefore, there is also the problem in that the throughput of the conventional system is small.
Moreover, in the system disclosed in Japanese Patent Laid-Open No. 5-245463, it is required to adjust the valve position in accordance with the concentration of vinyl chlorides in plastics to be treated and the revolving speed of the blade screw. Therefore, there is a disadvantage in that the dechlorination rate is greatly changed if the composition of plastics to be treated is changed. Moreover, in the above described system, dechlorination rate measurement are required to chemically analyze the objects, in order to determine how well the treated plastics have been dechlorinated. However, since such analysis is time consuming, it is difficult to adjust the system, and it requires a great deal of labor to determine whether the treated plastics can be used as a fuel.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a waste plastic dechlorination system, which can effectively remove chlorine from waste plastics containing vinyl chlorides.
According to the present invention, a waste plastic dechlorination system comprises: a dechlorination furnace having an inlet and an outlet for thermal-ecomposing a waste plastic containing vinyl chloride to dechlorinate the waste plastic; a rotating cutter provided in the dechlorination furnace; a pressure gauge for measuring a pressure in the dechlorination furnace; an exhaust apparatus connected to the dechlorination furnace via an exhaust pipe, for extracting a gas produced in the dechlorination furnace; and a control unit for controlling the exhaust apparatus in accordance with a signal outputted from the pressure gauge.
According to the present invention, the waste plastic containing vinyl chlorides introduced into the dechlorination furnace via the inlet is thermally decomposed and dechlorinated in the dechlorination furnace. During this time, the waste plastic is cut with the rotating cutter in the dechlorination furnace, and thermal-decomposition process proceeds. The pressure in the dechlorination furnace is detected by the pressure gauge, and the gas produced in the dechlorination furnace is exhausted by the exhauster.